Optical safety device



AWR l5, 194?. ALONG 2,418,845

I OPTICAL SAFETY DEVICE I Filed March l5, 1944 3 Sheets-Sheet 1 3 sheets-shed 2 J. A. LONG OPTICAL SAFETY DEVICE Filed March 15, 191545 OPTICA-L SAFETY DEVICE 3 Sheets-Sheet 3 equipment.

. a corporation of "mi atraen near. sanary non .lohn a. Long, Cambridge,v Mass., assigner to @Com-f bastion Control Corporation, ambridge, Mass.,

ssachusetts Application March l5, 1944, Serial No. 526,639

d Clie. (Cl. Z50-415) This invention relates to optical apparatus for observing heat sources, 4and more particularly to safety arrangements for photo'electrically supervising the operation of heating plants with respect to proper flame condition.

It is weil known that explosions are an everpresent hazard in the operation of heating plants such as boilers, heaters, furnaces, heat-treatment ovens, kilns and similar, especially pressure fed, Such explosions are mainly -due to failure promptly Vto detect loss of flame. As soon as the flame dies, fumes and gases accumulate and combine with air to form a highly explosive mixture in the combustion chamber. if only a few seconds elapse before the fuel is cut off, a stray spark, the hot; refractory lining, or another flame may set off the flash.

It is one of the main purposes of the present invention to provide a reliable safeguard against such dangerous conditions, by directly supervising a selectedl flame which may be a main ame, a pilot flame, or a combination of both, or other radiating body while, if desired, excluding interference with this function by. other radiators which need or Vshould not be included in the supervisory function; to provide equipment of this type which is suitable for a large variety of fuels such as oil, gas, pulverized coal; and generally to provide a device of this type which is able to y operate at relatively high ambient temperatures and can be conveniently combined with heating equipment of various types.

These and other objects and aspects will be more fully apparent from the following descrip-` tion of a practical embodiment illustrating the `genus of the invention. The descriptionA refers ,to a drawing in which i :i suitable material for example heat-resisting glass.

Suitably fastened to the wall is a mounting bracket 5 which has'an opening 6 approximately aligned with the furnace window 2 and to which lll valve 25. The cycle of operation may be initiated v by a thermostat, pressurestat, or manually by means of a push button, which devices are indicated at 28. An abnormal condition, as extinction of the pilot flame, may be indicated by a signaling device such as an alarm bell 29. The entire installation is supplied with electrical current from a supply network 3l?.

For the purposes of the present invention the flame to be supervised. in the present instance the pilot flame F, is preferably provided with an auxiliary radiating body which will be described more in detail hereinbelow and which may be fastened to the pilot burner by means of a Referring to Figs. 2, 3, and 4l,- the construction of the optical unit according to the invention will now be described in detail. The above-mentioned Fig. 1 is a schematic representation of a heat-` Fig. 6 a front elevation of the auxiliary radil ator.

The general arrangement and the environ ment of a practical embodiment of the invention will first be described with reference to Fig. 1 in which I represents a wall of a furnace which has a window i covered by a transparent plate t of mounting plate 5. with window t, carrieson its upper part a bracket 3i to which is hinged at 32 a support plate 33 which is provided with a flange te corresponding to an arm 35 extending from thelower portion of mounting plate b and having a slot 3Q which permits adjustment of the inclination of plate 33 relatively to mounting plate 5 and flame F by 'means of a screw bolt 3l inserted through a hole of flange 3i and through slot 36.

The lens plate 33 has a circular opening fitted with an optical mount tu astenedto. the plate with two rings il and i2 which have inside threads engaging the threaded boss i3 of aperture cone di. A lens 5B is confined between the wider end of cone di and flange 5I of ring tI.

The apex end of the cone dit has an aperture boss 55 pierced with a small aperture 60 and threaded on the outside.

An apparatus box 6i is fastened to the optical mount d!) and to the lens plate 33 by means of two rings t3, Si screwed to boss 55 confining therebetween the wall of box 6| which has at that point a circular window dimensioned to receive the boss; a stud 62 distances the lower portions of plate 33 and housing 6l.

Box 6i has a cover 66 and carries a chassis 61 upon which is mounted a radiation responsive device such as phototube 10. The box 6| may also contain, mounted on chassis al, suitable apparatus for amplifying the phototube output current, and relay apparatus whose construction depends upon the particular installation. Since the control circuit proper does not constitute part of the present invention, only the phototube is shown.

.The aperture cone 44 is' preferably so con-A structed that its inner surface fairly closely envelopes the light beam which lens D projects towards aperture 60 in the manner to be described below. rI'he cone is preferably provided with one or more cooling flanges indicated at 80.

The above-described arrangement operates as follows.

The auxiliary radiator 20 remains incandescent so long as the flame with which it is associated burns and will emit intense radiation predominantly of a wave length higher than that of the usual heating flame and well within the range to which conventional phototubcs are predominantly sensitive. On the other hand, due to its very small mass, the body 2li will cease to radiate practically immediately upon extinction of the flame. These radiators may cornprise, as shown in Figs. 5 and 6, a protective envelope 20a. for example of quartz, a radiating element 20h, for example a small platinum sheet or body of oxidized tungsten, sealed in the quartz envelope, and a supporting rod 20c.

Lens 50 is so placed relatively to radiator 2D that it images the latter at aperture 60; the photocell 'ill is arranged behind aperture 60 so that the effect upon cathode 16k, of the light flux coming from aperture 6D, is anl optimum under the prevailing conditions including the nature and shape of the cathode and the nature of the radiation in question.

Radiation coming from any region in fron of lens 50, other than that in the present embodiment occupied by radiator 2U, will be refracted by the lens to form beams which do not converge at aperture S0 and which do not conform 'to the shape of aperture cone M and are therefore inftercepted and absorbed by the inner cone surface which is preferably rough and blackened. For example, a point p below radiator 20 would be imaged at p' in image plane P and the respective beam intercepted as indicated. Similarly, a point between radiator and lens would be imaged beyond aperture G, and a point in front of the radiator would 'be imaged between lens and aperture; in either case only a small portion of the respective stray radiation will reach aperture 6U; by adusting, with conventional means, the sensitivity of the circuit including the photocell 'i0 to a minimum value above that of this stray radiation it is easily possible to render effective only the image of fully emitting radiator 20 at aperture 60.

In this manner, any effect upon the phototube oi radiation from furnace walls or from other more or less voluminous structural elements which might continue to radiate during a considerable time after extinction of the flame to be supervised, is effectively excluded. It will be understood that, if such structures as furnace walls or main burners were directly observed by the supervising photocell, the appreciable time required for cooling would allow accumulation of explosive mixtures before the .control arrangement respondedl Referring now also to Fig. 1,' the operation of an installation of this type may include the .following steps. With the pilot flame burning and auxiliary radiator 2D emitting, Vactuation of the controlling thermostat or of a manually operated switch will open the main solenoid valve l5 and the main flame will ignite. Upon actuation of the controlling element in the reverse sense, the main valve closes whereas the pilot flame continues to burn. If the pilot flame should fail at any time, regardless whether the main flame is on or off, the phototube 1U responds to` the instantaneous cooling of auxiliary radiator 20 and the relay circuit closes the automatic pilot valve if the mainflame is off, or both valves `if the latter is on during extinction of the pilot flame.

It will be evident that the mass of radiator 20 can be kept very small since the efciency of its effect upon the phototube is very high; this small size permits full utilization of the above described selective effect of the aperture 6D.

On the other hand, there is sufficient leeway in selecting the mass of the radiator so that rapid fluctuations of the flame such as due to flutter can be rendered harmless by a certain time lag between such flame fluctuations and the corresponding variation in radiation intensity of element 20. It is indeed easily possible to select the mass ofthe radiator with a view to eliminate the effect of flame fluctuations within a given maximum range, whereas all longer fluctuations will cause cooling of element 20 to such an extent that the phototube circuit will respond.

It will be understood that a cylindrical tube with an aperture baille, as indicated at 44a of Fig. 5, offers to 'a certain degree the above-mentioned advantages, and might sometimes be used to advantage; however it will now be obvious that a conical aperture tube is more favorable since it absorbs the undesired radiation as far from the aperture as possible, thus increasing the temperature gradient between heat source and supervisory apparatus. The constrictecl cross section near the aperture, constituting a bottle neck regarding heat conduction, serves a similar purpose.

It willalso be understood that instead of one heat dissipating fin 8B, several such elements, or means having analogous effect may be used. Under favorable conditions the aperture tube alone is able to .dissipate the heat and the fln can be omitted.

The emission range of a radiator of the type herein referred to compares, as to photoelectric effectivity; very favorably with that of most heater flames which radiate mainly in the photoelectrically rather ineffective blue range although they might appear yellow due to the comparatively high sensitivity of the visual apparatus to that range. Further, the high absolute intensity of the radiation from the auxiliary emitter provides more reliable operation and permits the use of less sensitive and hence cheaper and more rugged photoelectric, amplificationA and relay equipment. The intensity of the auxiliary radiator` is also sufllciently high to penetrate considerable blackening of transparent window clo sures such as shown at 6 of Fig. 1.- f

It will be further understood that use of arrangements according to the invention. is not restrictedto pressure fuel equipment but that it can be advantageously applied to any heating system which presents analogous problems of suananas pervision and control. Also, the` auxiliary radiclosureris for the purpose of illustration only and that this invention includes all modifications and equivalents which fall within the scope of the appended claims.

I claim:

1. In apparatus for photoelectrically supervising a ame within conning walls having an observation window, a mounting plate having an opening adapted to surround said window, a second plate having a lens mounted therein hinged to said mounting plate at a distance therefrom thereby securing free passage of air between said plates, a housing having a phototube mounted therein, and a light conning conduit support- -ingly connecting and spacing said lens plate and said housing, said hinged connection permitting the uniplanar alignment of said phototube with said flame, and said spacing inhibiting the transmission of heat to said phototube.

2. In apparatus for photoelectrically supervising a flame within confining walls having an observation window, a mounting plate having an opening adapted to surround said window, a second plate having a lens mounted therein hinged to ,said mounting plate at a distance therefrom thereby securing free passage of air between said plates, a housing having a. phototube 4mounted therein, and a light conning conduit supportingly connecting and spacing said lens plate and said housing, said hinged connection permitting the pivoting of said housing on said mounting plate for the purpose of aligning said lens and said phototube with said name.

3. In apparatus for photoelectrically supervisservation window, a mounting plate having an opening adapted to surround said window, a second plate having a lens mounted therein hinged f ing a llame within conning walls Ahaving an ob- I which secures free passage of air between said plates,v a housing having a phototube mounted therein, and a light conning conduit supportingly connecting and spacing said `lens plate and said housing, s aid hinged connection permitting the pivoting of said housing on said mounting plate for the purpose of aligning said lens and said phototube with said flame, and adjustable locking means connectingsaid mounting plate with said lens plate for the purpose of maintaining said alignment.

4. In apparatus for photoelectrically supervising a ame within confining walls having an observation window, a mounting plate having an opening adapted to surround said window, a second plate having a lens mounted therein, said second plate hinged to said mounting plate'at a distance therefrom which provides free air pas" sage between said plates, a housing having a photoelectric tube mounted therein, a light conning conduit -supportingly connecting and spacing said second plate from said housing, a heat radiation n annularly mounted in said conduit member between saidsecond plate and said housing, locking means connecting the said plates together with the said hinge comprising -means for adjusting the-vertical angle of the said The following references 'are of record in the I ille of this patent:

UNITED STATES PATENTS Number Name Date 2,302,554 Kingsbury v.- Nov. 1'7, 1942 1,639,534` Ruben'.4 Aug. 16, 1927 1,994,860 Matson' Mar. 19, 1935 2,292,243 Schwartz Aug. 4, 1942 2,007,714- Gauger July 9, 1935 2,306,073 Metcalfe; Dec. 22, 1942 "151229414 Huiile'r et al.v July 5, 1938 Schumann et al Oct. 10, 1944 

